This paper deals with Google App Engine, which is a cloud platform for development and hosting web applications on Google infrastructure. It also discusses NoSQL databases, especially MongoDB database. High Replication Datastore, a production datastore for Google App Engine, is not available in local environment. The solution is the use of so-called datastore stubs, which store data to some available local datastore and simulate real production datastore. In Google App Engine, two datastore stubs are released: Datastore File Stub and Datastore SQLite Stub. In this paper Datastore MongoDB Stub is introduced, which is a new possibility to use with Google App Engine in development on local environment. Results of several experiments comparing performance of Datastore File Stub and Datastore SQLite Stub to the new Datastore MongoDB Stub are presenterd too.